. [Reports]. nonand is best accounted for by ocean scour, through which some ofthe soft sediments were removed, before the overlying sedimentswere introduced. This same phenomenon has been noted in otherCambrian formations of the Ozark regkn^ especiallyIhe Jeffer-son City. j SUN CRACKS. These are irregular polygonal markings exhibited on the sur-faces of some beds, either in the form of low ridges or shallow de-pressions. ^> Soft clayey sediments shrink and crack when dried. Thisfrequently happens during short periods of emergence of areasalong the sea shore. During the succeeding period of
. [Reports]. nonand is best accounted for by ocean scour, through which some ofthe soft sediments were removed, before the overlying sedimentswere introduced. This same phenomenon has been noted in otherCambrian formations of the Ozark regkn^ especiallyIhe Jeffer-son City. j SUN CRACKS. These are irregular polygonal markings exhibited on the sur-faces of some beds, either in the form of low ridges or shallow de-pressions. ^> Soft clayey sediments shrink and crack when dried. Thisfrequently happens during short periods of emergence of areasalong the sea shore. During the succeeding period of submergencethese cracks are filled with other sediments thus preserving thestructure. The Davis formation, more than any of the others, exhibitsthis phenomenon. The markings referable to this cause are notas well defined as one might expect, altho they are abundant incertain parts of the formation. The shale beds are covered with ma Missouri Bureau of Geology and Mines. Vol. IX., Series 2, Plate XVII. LEGEND. Eighteen inches of alternating shale, limestone and chloritic limestone. Shale inlower left-hand corner is soft. Mine No. 2, Doe Run Lead Co. STRUCTURES. 75 what are commonly called fucoidal markings, there being an al-most infinite variety of these. rTneshaly horizons of the Doerun formation exhibit a varietyof markings which may be due in part to sun cracks. However,many of them are considered to be fucoidal markings. FOLDING AND FLEXURING. Flexures or folds in sedimentary rocks may be due either tothe conditions under which original deposition has taken place;to settling as a result of solution; or to later compressive Hise* has pointed out that below a depth of 10,000 metersrocks are deformed by flowage. Above this-, deformation is bycombined fracture and flowage. Flowage may even occur at thesurface, .under favorable conditions. In the area under-discussion folds due to solution and in-equalities in the sea floor upon which the sediments were depositedan
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